Hitherto, a pump for allowing a working fluid to flow has included a check valve as a resistance element in a fluid flow pass. Particularly, there are check valves adopted for a small motor for changing the volume of a pump chamber by a piston or a diaphragm for allowing a working fluid to flow.
As the first related art, a structure of a check valve made up of a pump suction and discharge unit having a suction port and a discharge port of working fluid, a pump valve seat unit having a suction side check valve and a discharge side check valve, and a pump actuator unit with the pump valve seat unit fixed via an O ring as a sealant between the pump suction and discharge unit and the pump actuator unit and a pump including the check valve is known as a structure for controlling working fluid when the working fluid is sucked into a pump chamber, and discharging the working fluid into the outside of the pump chamber (JP-A-10-220357).
As the second related art, a check valve including a valve seat, a ball on the suction side of a working fluid for opening and closing the valve seat, a stopper with an opening for limiting the movement amount of the ball, and a joint member for assembling the valve seat and the stopper into one piece is known as a check valve in a fluid flow pass for sucking the working fluid into a pump chamber and allowing the working fluid to circulate only in one direction in discharging the working fluid into the outside of the pump chamber. Further, the check valve is pressed against and fixed to a pump case by a press member. A pump including a pair of the check valves on the suction side and the discharge side of the working fluid is also known (JP-A-2000-2350).
Further, as the third related art, a check valve made up of a valve seat formed in a pump housing, a ball for opening and closing the valve seat, a ball stopper for limiting the movement amount of the ball, and a coil spring for pressing the ball against the valve seat and a pump including the check valve are known (JP-A-2001-173816).
However, in the invention described in JP-A-10-220357, when the pump valve seat unit includes the suction side check valve and the discharge side check valve, the size in the plane direction increases. Since the pump valve seat unit is sandwiched between the pump suction and discharge unit, and the pump actuator unit via the O ring and is fixed, the pump performance may become unstable because the pump chamber space area is not constant.
Further, the sealing property of the O ring can degrade with the use of the O ring for a long term. Also, it is inconvenient to replace the O ring at regular time intervals and the inconvenient to consider the chemical resistance depending on the type of working fluid and change the material of the O ring.
The pump valve seat unit is molded of a synthetic resin and the suction side check valve has a structure wherein a separation section of a suction section and a discharge section of fluid floats above the pump chamber. Thus, when the actuator is driven, the pump valve seat unit becomes deformed and a predetermined pressure in the pump chamber cannot be provided. The valve seat also wears as working fluid flows and a flaw can easily occur because of cavitation, etc., which causes insufficient durability.
In the invention described in JP-A-2000-2350, the ball is included in the space provided between the valve seat and the stopper, and moves in the space, to thereby open and close the valve seat. However, the gap between the ball guide wall of the stopper and the ball is small, and movement of the ball is hindered because of contact resistance. Since there is rapid change in the opening width on the seating face of a working fluid outflow section of the valve seat, a vortex may occur which inhibits the smooth flow of the working fluid.
Since the ball is molded of cemented carbide or ceramics, and the weight per unit volume is larger than that of a general working fluid, the ball is hard to move when opening and closing the valve seat. Thus, the check valve is unsuitable for a small pump for making the working fluid flow out at a high frequency using a diaphragm, for example.
Further, in the invention described in JP-A-2001-173816, the check valve has a structure wherein the ball is pressed against the valve seat side by a coil spring at all times and the valve seat is opened with the pressure of the working fluid, and is closed by the elastic force of the coil spring. Thus, the inflow pressure into a fluid inflow path requires a considerable size for the elastic force of the coil spring and the weight of the ball, and it is difficult to adopt the check valve as a small check valve for opening and closing the valve seat based on the inertance value difference between the inlet flow pass and the outlet flow pass of working fluid, for example.
In such a pump, a coil spring is included in the flow pass of the working fluid in the check valve and thus the flow of the working fluid is inhibited by the coil spring. Further, the fluid flow pass is curved rapidly from the check valve and thus the flow resistance of the working fluid increases.
It is therefore an object of the invention to provide a check valve which has a simple structure and a good assembly property that can be provided at low cost. It is also an object of the present invention to provide a small, durabile, and high-performance pump including the check valve.